Saltalamacchia, 27, is hitting .236 with a .292 OBP, .509 slugging mark and .801 OPS along with 20 homers, the most by any catcher in the majors. He is not eligible for free agency until after the 2013 season. Shoppach, meanwhile, has delivered outstanding production, hitting .258/.346/.508/.854 with five homers in 43 games.

With Ryan Lavarnway seemingly big league-ready in Triple-A (a notion reinforced by his call-up on Wednesday), there was a strong sense that the Sox might part with one of the team’s major league catchers — most likely Shoppach — in order to turn a player under team control for the short-ish term (Shoppach for just two more months, Saltalamacchia for the next season and a third) into a long-term asset in the form of some kind of prospect return.

Shoppach seemed the most likely to go, since Lavarnway could come up, partner with Saltalamacchia and replace Shoppach’s right-handed thump while continuing his catching apprenticeship at the highest level. Shoppach was signed to a very affordable (indeed, bargain level) one year, $1.35 million deal, making him a player who would fit onto just about any team’s roster, given the level of production and cost.

So why didn’t it happen? Why wasn’t Shoppach (or one of the other catchers) dealt?

According to a team source, the answer related primarily to the need for offense at a time when David Ortiz remains on the disabled list. In recent days, the team has had both Shoppach and Saltalamacchia in the lineup not because it was showcasing either for a trade but instead because there was an effort to get as many impact bats as possible into the lineup at a time when Ortiz — the AL leader in OBP, slugging and OPS — is on the shelf.

Secondarily, the team is aware of the inherent vulnerability of catchers, something that can wipe out the appearance of depth in a hurry. A year ago, after all, the Sox gave Lavarnway his first two big league starts at catcher on the final two days of the season — the most important of 2011 — because in the span of a couple days, both Jason Varitek and Saltalamacchia were injured. Two years ago, the team ended up making an emergency trade for Kevin Cash at a time when both Victor Martinez and Jason Varitek were injured within days of one another.

Still, concerns about depth lagged behind that of the desire for offense.

And so, all three catchers remained on the roster, and with Shoppach suffering a shin injury on Tuesday that may render him unavailable on Wednesday, the Sox are currently carrying Saltalamacchia, Shoppach and Lavarnway on the roster. They may maintain that alignment for a bit, since the presence of three catchers on the roster will permit the Sox to use one of those players as a DH while Ortiz is out.

One footnote: The Sox are aware of the extreme disparity in the team’s record in games started by Saltalamacchia (29-38, .433) and Shoppach (24-13, .649) behind the plate. However, as eye-opening as those numbers might seem, the team considers the vast difference in results fluke-ish, as discussions with the uniform personnel (pitchers, coaching staff, etc.) suggested no red flags in Saltalamacchia’s work behind the plate that might explain the team’s sub-.500 record on days when he starts behind the plate.